My most recent video post was an introduction to the topic of battery innovation. Donald Sadoway from MIT explains that in our current energy grid, the energy supplied must be in constant balance with the energy demanded. This principle poses a challenging technical difficulty in implementing renewable energies on a full scale. Because wind and solar power do not produce a constant flow of energy, when the sun goes down or when the wind stops, energy supply from these sources drops below energy demand. Immediately this difference in energy supply and demand needs to be contributed to the grid by other generators or grid storage but there is a infrastructural problem:
Today, 99 percent of grid storage takes the form of “pumped hydro”—water is pumped uphill to a reservoir and released to turn a generator when energy is needed. This low-tech method is efficient, and it’s cheap over the long term, but it’s limited to places with mountains and readily available water. As a result, it provides less than 1 percent of the power capacity in the United States on a given day, according to Mark Johnson, director of the grid storage program at the Department of Energy’s ARPA-E research agency.
Coal and nuclear plants are not fast enough and current grid storage is inadequate to supply this difference, but as Donald concludes, new forms of batteries could be the key to solving the renewable intermittancy problem.
Molten Metal Batteries
Innovations in battery technology could potentially make renewables a comparable energy source to coal and nuclear, but batteries today do not meet the demanding performance requirements of the grid. A feasible battery would have to be able to recharge, withstand uncommonly high power for a long time, all at a low cost. Donald Sadoway presents a new technology that may flip the switch for renewable energy. Traditional batteries use two solid metal electrodes and an electrolyte solution that transfers electrons between the two electrodes. Understanding the economies of scale gained by current aluminum metallurgy (conversion of bauxite ore into metal aluminum), Donald considered a new compositional state of the traditional battery. Instead of using two solid state electrodes and a liquid solution of electrolytes, Donald proposed a high temperature battery using two varying density molten metal electrodes and a molten salt electrolyte to facilitate the transfer of electrons. The incoming currents are strong enough to keep these metals in molten state. Quoting an article on Technology Review about Donald and his company “Ambri”, the advantages of this technology are apparent:
Conventional rechargeable batteries have solid electrodes that degrade with use, but a battery with only liquid parts could last for years without losing much of its energy storage capacity. The molten materials can also operate at much higher current densities than solids, and for longer periods of time.
The molten composition of this battery provides the durability and capacity to perform on our power grids. This diagram shows rough representation of the chemical energy exchange between low density high density liquid metals in a molten salt medium similar to Donald’s.
The most recent development in battery technology has yielded a rechargeable battery with the highest storage capacity of any battery to date. The technology, developed by Stuart Licht, Baochen Cui, Jessica Stuart, Baohui Wang, and Jason Lau, at George Washington University, is called Molten-air. Similar to Donals Sadoway’s Molten metal technology, Molten-air batteries are rechargeable and operate at high temperatures with a molten electrolyte. The difference is that molten metal batteries use a molten metal cathode, whereas Molten-air batteries use ‘free’ oxygen from the air as a cathode. This not only makes these batteries substantially lighter and less material intensive, research also shows that these batteries have extremely high capacity and have excellent recharge capabilities. Stuart Licht and his group at George Washington University has demonstrated 3 viable chemistries for this technology. Their composition and storage capacity are shown in the following table:
More research still needs to happen in order to optimize this technology. Molten air batteries have potential to displace Donald Sadoway’s molten metal batteries because of their advantages (more capacity, less material intensive).
These technologies are great examples of how innovation will accelerate the switch in energy dependency from fossil fuels to renewable sources. With these new batteries and their large storage capacities solar power will be able to power homes even when the sun isn’t shining. The future is looking bright.